For various reasons, it may be desirable to simulate a real aircraft flight environment via a flight simulator. A flight simulator may simulate a real aircraft flight environment by exposing a pilot in training to important aviation stimuli that may be present in an actual flight environment, thus allowing the pilot to be trained in aircraft flight conditions without any of the risks inherent in actual flight. As an example, a flight simulator may display a HUD that accurately simulates a real aircraft HUD.
A real aircraft HUD displays flight information to a pilot which is projected or otherwise graphically overlaid upon the pilot's view out the cockpit windshield. As an example, a real aircraft HUD may display geographic information. As another example, a real aircraft HUD may display visual targeting elements, such as aiming reticles that correspond to real out-of-window objects.
A pilot in a real aircraft cockpit typically perceives out-of-window objects at near optical infinity, i.e., the light rays from the objects are parallel when they arrive at the pilot's eye. Accordingly, standard design of a real aircraft HUD usually includes displaying images near optical infinity, thus reducing need for a pilot to refocus while shifting between viewing HUD images and real out-of-window objects. Further, a HUD displaying images near optical infinity may also remove or reduce parallax between HUD images and real out-of-window objects. For example, as a pilot shifts head position, relative position between an out-of-window point and a point in a real aircraft HUD image will remain visually fixed.
A standard real aircraft HUD system usually displays images via an optical combiner glass including a holographic element that projects images within a characteristic field of view (“FOV”). HUD images viewable by a pilot may be limited by the pilot's head position relative to a viewed HUD combiner glass. For example, a pilot may shift head position, either right or left, up or down, to the front or back, far enough to cause part of a HUD image to disappear. In other words, HUD images viewable by a pilot in a real aircraft are dependent on the pilot's head location within what is known as the HUD “viewing volume”, which is alternately called the HUD “head box”.
A standard flight simulator usually includes a viewing screen that simulates a pilot's view from a real aircraft cockpit, and also may include a HUD. Current flight simulator HUDs are available in various configurations. For example, a flight simulator HUD image may be superimposed onto a viewing screen. As another example, a flight simulator may include a combiner glass in between a viewing screen and a pilot, projecting HUD images at near optical infinity. As yet another example, a reflective HUD includes a reflective combiner glass that reflects HUD images that are sourced from a separate display. Such a HUD display may be distanced from the reflective combiner glass, such that HUD images viewed by a user may have an optical focus distance comparable to a distance between the pilot's eye and the viewing screen.
However, current flight simulator HUD configurations typically do not accurately simulate all of the characteristics of a real aircraft HUD. For example, merely superimposing a HUD image onto a viewing screen may not simulate limitations of the HUD viewing volume, because the pilot in the simulator will see the HUD images from all viewing angles (the pilot's FOV not being limited by the optical combiner as would be the case in a real aircraft). Further, a HUD projecting images near optical infinity may result in unrealistic parallax caused by a pilot's head movement, because the flight simulator screen is typically much closer than the objects would be outside a real aircraft, on the order of 1-2 meters from the pilot. Further still, although a reflective HUD may project images focused at short distances, a reflective HUD may inefficiently add to flight simulator cockpit volume, once packaging options are considered. Even further, a reflective arrangement of this type also generally fails to accurately simulate the limited viewing volume of a real aircraft HUD. Additionally, current flight simulator HUDs typically include holographic elements that are expensive.
For the reasons described above, among others, there exists a need for a flight simulator HUD that accurately simulates HUD images, represents the limitations of a real aircraft HUD viewing volume, is appropriately focused to a viewing screen distance to remove parallax, and does not include holographic elements, while simulating a real cockpit volume.